The invention relates to a valve-controlled positive displacement pump having valve triggering, which permits the positive opening or keeping open of an inlet valve, operating in the manner of a non-return valve, of a displacer working space, so that the displacer working space can be connected to the inlet side of the unit even during the working stroke of the displacer and can be shut off from the outlet side of the unit by its outlet valve, which remains closed when the inlet valve is open.
German Patent Document DOS 3,028,396 discloses an appropriate piston pump having piston working spaces arranged in series. Special fluid members can be used forcibly to lift the suction valves out of their closed position or to prevent them from reaching the closed position. As a result, the respective pistons are prevented from doing effective pumping, because it is not possible to build up an effective pressure in the piston working spaces.
The delivery rate of the pump can be matched very quickly to the respective requirements by means of the suction valve triggering, without the need to shut down the pump or its drive.
Again, there are in principle other possibilities for quickly shutting down the delivery flow of a piston pump.
For example, a pump can work, if necessary, in so-called circulating operation, in which it is achieved by appropriate control of a reversing valve that the medium delivered by the pump flows back by a short path to the suction side or to a reservoir arranged on the suction side, and is not fed to the respective load on the pressure side of the pump. A corresponding arrangement is represented with reference to a radial piston pump in German Patent Document DOS 2,425,022. In this case, the reversing valve is controlled as a function of the pressure applied to the load, it being the case that upon the reaching of a first pressure threshold value initially only a restriction of the flow on the suction side of the pump is formed, in order in this way to reduce the delivery rate of the pump. As soon as a second pressure threshold value is then reached on the pressure side of the pump, a switch is made to circulating operation, so that the pump no longer works effectively.
It is known from British Patent Document 1,413,998 to provide two piston working spaces whose pistons work in anti-phase with a connecting line which can be shut off. The pump works in the normal way in the closed state of this connecting line. As soon as the connecting line is opened and a flow is enabled in both directions, the pumping medium is shifted back and forth continuously between the two piston working spaces, because the pressure stroke of the piston in one piston working space coincides with the suction stroke of the piston in the other piston working space. Consequently, the pumping medium displaced from the one piston working space is received by the other piston working space. In this way, the pump is prevented from working effectively.
If necessary, it can be provided in accordance with British Patent Document 1,413,998 to arrange a non-return valve in the connecting line, so that after opening of the connecting line only a flow in one direction is enabled. The consequence of this is that during the pressure stroke of the piston in one piston working space the pumping medium can be shifted from this piston working space into the other piston working space, whose piston is executing a suction stroke. As soon thereafter as the direction of movement of the piston is reversed, the medium displaced by the other piston, which is now in the pressure stroke, cannot flow back through the connecting line--it is, rather, expelled to the pressure side of the pump by the pressure valve assigned to the other piston. In this way, the working of only one piston is rendered virtually ineffective, that is to say the delivery rate of the pump is halved.
A stepped control of the pump can also be undertaken in this way. The first step is, for the purpose of reducing the pumping capacity, to release only one connecting line having a non-return valve in order to reduce the delivery rate of the pump. Thereafter, a connecting line which allows flow in both directions can then be released in order to switch the pump to become ineffective.
U.S. Pat. No. 3,682,565 shows a radial piston pump whose pistons are loaded by means of springs against an eccentric which drives the pistons and whose circumference interacts with the facing end faces of the pistons. The piston working spaces each have a pressure valve which is arranged on the pump housing coaxially with the respective piston and whose valve body controls a bore coaxial with the piston. The suction valves are arranged in each case on the piston side, the suction valve body in the associated piston controlling an axial bore which communicates via radial bores in the piston with the eccentric working space, which forms the suction side of the pump or is connected thereto. Arranged on the pressure side of the pressure valves are relief valves which in normal operation connect the outlet side of the pressure valves to the pressure side of the pump or to the load connected there. As soon as a pressure threshold value is reached, the respective relief valve reverses, the outlet side of the pressure valve of the respectively assigned piston working space being connected to the suction side and simultaneously shut off from the pressure side of the pump or from the load connected there.
It is achieved in this way that individual pistons or all the pistons of the pump are unable to deliver any pumping medium to the pressure side or to the load a soon as the pressure threshold value is reached.
German Patent Document DOS 3,740,672 discloses a valve-controlled piston pump in which the piston working spaces are assigned in each case a separate outlet valve upon the opening of which the piston working space is connected to the suction side of the pump. Consequently, a similar effect is achieved as in the case of suction valve triggering.
For the rest, reference is made to the technological background to be seen in German Patent Documents DOS 3,240,405; DOS 3,504,163; and DOS 1,653,632.
It is an object of the invention to provide a positive displacement pump equipped with valve triggering, whose design is also well suited for realizing a radial piston pump having triggering of the inlet valve, that is to say having suction valve triggering.
This object is achieved according to preferred embodiments of the invention by providing an arrangement comprising a:
valve-controlled positive displacement fluid device arrangement having valve triggering, which permits the forced opening or keeping open of an inlet valve, operating in the manner of a non-return valve, of a displacer working space, so that the displacer working space can be connected to the inlet side of the unit even during the working stroke of the displacer and can be shut off from the outlet side of the unit by its outlet valve, which remains closed when the inlet valve is open,
wherein the displacer includes a piston which is spring-loaded against an eccentric which drives it,
wherein the associated inlet valve is arranged on the piston and controls by means of its valve body an inlet opening penetrating the piston from a space on the inlet side to the piston working space,
wherein the eccentric or a sleeve-like part arranged on its circumference is axially displaceable, and
wherein arranged on the circumference of the eccentric or of the sleeve-like part are axially adjacent regions whose otherwise identical cross-sections have different diameters, it being the case that in one axial position of the circumference the region having the larger diameter keeps the inlet valve body away from its closed position in the manner of a stop, whereas the other region having the smaller diameter becomes effective in another axial position of the circumference and permits closure of the inlet valve body.
The invention is based on the general idea of controlling the mobility of the inlet valve body by elements on the eccentric side which, for their part, can be switched to become effective or ineffective by axial displacement in the direction of the axis of rotation of the eccentric.
It is advantageous in this case that the invention can be directly realized with radial piston pumps, because essential parts of conventional radial piston pumps can be taken over virtually unchanged. Consequently, the invention is explained below principally with reference to pumps.
Nevertheless, the invention is not restricted to pumps. Rather, preferred embodiments of the invention can also advantageously be used with hydraulic motors and serve there to vary the motor displacement.
In order to apply the invention in the above-mentioned radial piston pumps, it is essentially sufficient to construct the suction valve such that the suction valve body can interact with the above-mentioned regions on the circumference of the eccentric or of the sleeve-shaped part.
According to a preferred embodiment, it can be provided for this purpose that there is arranged on the suction valve body an extension or stem which is directed against the eccentric and which interacts with the regions of different cross-section on the circumference of the eccentric or of the sleeve-shaped part in such a way that the suction valve is able to close when the region of smaller cross-section is pushed into the zone of movement of the extension or stem, while the extension or stem bears against the region of larger cross-section before the closing position of the suction valve body is reached when the eccentric or the sleeve-shaped part is correspondingly axially displaced.
In a particularly preferred embodiment, it is possible to arrange on the circumference of the axially displaceable eccentric or of the axially displaceable sleeve-shaped part a circumferential groove, which can be relatively displaced by displacing the eccentric or the sleeve-shaped part into the region of movement of the extension or stem, and thus enable closure of the suction valve body.
In this embodiment, the circumferential regions of the eccentric or of the sleeve-shaped part, which axially adjoin the circumferential groove, can serve in all axial positions of the eccentric or of the sleeve-shaped part to guide and to drive the pump piston or the pump pistons and moreover, given appropriate displacement of the eccentric or of the sleeve-shaped part, take over the function of a stop, interacting with the extension or stem of the suction valve body, in order to prevent the suction valve body from assuming its closing position.
The above-noted circumferential groove is likewise able to take over a double function by, on the one hand, permitting closure of the suction valve body in the corresponding axial position of the eccentric or of the sleeve-shaped part and, on the other hand, producing between the eccentric or sleeve-shaped part and the eccentric-side end face of the piston in this operating state, a channel suitable for the passage of pumping medium which communicates with a suction opening in the piston or piston cap that is controlled by the suction valve body.
Embodiments are contemplated with construction of the piston-side opening controlled by the suction valve body as an axial bore of the piston and connecting it to the eccentric working space, which is constructed as the suction side of the pump or is connected to a suction port of the pump, without appreciable restriction.
The same basically applies when instead of the circumferential groove a circumferential stage or protrusion is arranged on the circumference of the eccentric or of the sleeve-shaped part, so that a region of the eccentric or of the sleeve-shaped part of small cross-section is formed on the one side of the circumferential stage, and a region of larger cross-section is formed on the other side.
One side wall or both side walls of the circumferential groove can also be constructed as a cone. Again, a conical region can be provided instead of a circumferential stage having a steep transition between the regions of different cross-section. It is possible in this way in the case of axial displacement of the eccentric or of the sleeve-shaped part to open a previously closed suction valve relatively slowly by virtue of the fact that the extension or stem of the suction valve body slides onto the conical region during axial displacement of the eccentric or of the sleeve-shaped part.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.